Lead zirconate titanate is a perovskite, wherein the A sites of the perovskite are occupied by bivalent lead (Pb2+) and the B sites of the perovskite are occupied by tetravalent zirconium (Zr4+) and tetravalent titanate (Ti4+). PZT is doped in order to influence an electrical or piezoelectric property such as permittivity, Curie temperature, coupling factor or piezoelectric charge constant (d33 coefficient, for example).
A piezoceramic component in the form of a monolithic multilayer actuator is known from EP 0 894 341 B1. The multilayer actuator consists of a plurality of piezoelectric elements arranged one on top of the other to form a monolithic stack. Each of the piezoelectric elements has an electrode layer, a further electrode layer and a piezoceramic layer disposed between the electrode layers. Piezoelectric elements adjacent to one another in the stack each have a common electrode layer. The electrode material of the electrode layers consists of a silver-palladium alloy. The piezoceramic layers have a piezoceramic material made of PZT. The calculated empirical formula of the piezoceramic material is Pb0.99Ag0.01La0.01[Zr0.30Ti0.36(Ni1/3Nb2/3)0.34]O3, as follows. A piezoceramic powder of the nominal composition Pb0.99La0.01[Zr0.30Ti0.36(Ni1/3Nb2/3)0.34]O3.005 is produced in accordance with known methods. Green films are prepared therefrom, provided with electrode material, layered to form the corresponding stacks, laminated and sintered under identical conditions. A piezoelectric actuator of high strength is obtained, for which a Curie temperature of 170° C. is determined. This actuator can therefore be used in a temperature range up to a maximum of about 80° C. This piezoceramic or, respectively, the piezoelectric actuator of multilayer design produced from it, possesses a complex doping with nickel and niobium for the B-site, as can be seen from the formula.
The composition of the piezoceramic material resulting from the sintering process is stoichiometric. The stoichiometry is a result of the fact that in the course of the sintering excess lead escapes in the form of lead oxide (PbO). Excess heterovalent lanthanum present is compensated by the inward diffusion of silver from the electrode material into the A sites of the PZT.
The resulting multilayer actuator is characterized by good piezoelectric properties. For example, the Curie temperature Tc is approximately 170° C. That said, however, the sintering temperature required in order to obtain the good piezoelectric properties is in excess of 1100° C. In order to avoid fusing of the electrode material at these high sintering temperatures the palladium content of the electrode material must be at least 30 weight %.
For reasons of cost it is desirable to reduce the palladium content of the electrode material or to use generally cheaper electrode material such as copper or pure silver. Each of these metals has a melting point below 1100° C. This means that the sintering temperature must be lowered. The known piezoceramic composition is not suitable for compressing at a sintering temperature of less than 1100° C. The improved piezoelectric properties are not achieved at such a low sintering temperature.